guys I have a few you tube channels you need to check out the 1st is "project farm" this guy does testing himself and he sends out samples to get all the techno numbers, he did a comparison on most synthetic oils, froze them, heated them up, can't really explain but good to watch, he did all the big names and there were a few surprise front runners and bottom runners, just as an example amsoil,pensoil,redline,royal purple, mobil one and a bunch more, I bust the bubble by saying amsoil won, 2nd was pensoil, the other is "keep it dirty" this guy lives out west, runs the crap out of his truck, has all kinds of upgrade videos from led license plate lights to front and rear suspension, fluid changes, and I am glad I watched the oil change because he didn't take skid plate off and oil went every where LOL. he has a video on diff cover, he put in 75w-110 amsoil, 140 for heavy towing, also mentioned spicer cover but also said this cover might void your warrantee if they want to be *****, even though it is made by dana also just the tag is different, found the ford version for $208, spicer was $140, didn't take the chance and bought the ford version, also remember the new cover almost takes 4 quarts, original was 2.7